Three-phase bridge rectifiers or diode bridges can include three series-connected pairs of diodes connected in parallel, which interconnect a three-phase AC voltage source with a DC load.
A functioning diode can have a very low resistance in one (conducting) direction of current flow and a very high resistance in the other (blocking) direction. As any electronic components, diodes can be subjected to wear and sometimes can become faulty. A common fault can be a so-called shorted diode, in which the very high resistance in blocking direction degrades and the diode conducts in both directions.
Because a shorted diode fault can lead to high currents in the bridge rectifier and the connected equipment, after a detected shorted diode fault, the input current and/or the output current of the bridge rectifier can be quickly shut down so that a detection of such a fault can be made.
For example, in US 2011/0216449 A1, the voltage across a pair of diodes can be measured to determine a ratio between the individual diode voltages. This ratio can be analyzed, to determine whether one of the diodes has a fault.